Various application require a sensor to detect an angular position of a shaft, in which an angle in excess of 360° needs to be detected. For example, an angular position may be detected in combination with a number of revolutions of an input shaft.
It is known in the art to use a counter for counting the revolutions of a code carrier which is driven by the shaft. In another approach, it is known to provide a multiturn angular position sensor by actuating a plurality of gear stages with the input shaft. Thus, different gear transmission ratios can be used for measuring the multiturn angle by observing multiple angles, associated with the different gear transmission ratios, in which each observed angle has a different relation to the multiturn angle of the input shaft to be determined.
For example, it is known in the art to provide a multiturn rotary encoder for determining an angle of rotation of a shaft with respect to a predetermined reference that can exceed 360°. For example, U.S. Pat. No. 8,154,427 discloses such multiturn rotary encoder comprising a single-turn unit that includes a code carrier and a single-turn evaluation unit for processing single-turn position signals to form a single-turn code word, and a first multiturn unit, including at least one first multiturn code carrier and a first multiturn evaluation unit for processing first multiturn position signals to form a first multiturn code word that indicates the number of revolutions covered by the input shaft. The device also comprises a second multiturn unit, including at least one second multiturn code carrier and a second multiturn evaluation unit for processing second multiturn position signals to form a second multiturn code word that likewise indicates the number of revolutions covered by the input shaft. The multiturn code words may thus be generated independently of each other, and the functioning of the multiturn units may be ascertained by the two multiturn code words.
It is also known in the art to determine an axis using a magnetic sensor. In such prior art devices, a magnet may be mechanically linked to a gear wheel, and a magnetic sensor is used to determine the angular position of the magnet. For example, different magnetic sensors may detect the magnetic field, e.g. a magnetic field orientation, of corresponding magnets linked to corresponding gear wheels, in which each gear wheel has a different gear transmission ratio with respect to a hub gear wheel mechanically connected to an input shaft. These magnetic sensors use the nonius principle to come to an accurate angle determination. Thus, a multiturn angle of the input shaft can be detected if appropriate different gear transmission ratios are used.
For example, U.S. Pat. No. 7,637,020 discloses a rotation angle sensor for determining an absolute angular position of a body that can rotate through several rotations. The sensor includes two code wheels which rotate as the body rotates. The code wheels are driven at a different gear ratio such that the code wheels rotate faster than the body and the code wheels rotate at different rates. Two sensor elements respectively determine the rotational angle positions of the code wheels. The difference between the rotational angle positions is a beat angle. The different gear ratio is selected such that beat angle periods are in an angular measuring range of the sensor and the absolute angular positions of the code wheels in the beat angle periods is different. The absolute angular positions of the code wheels in successive beat angle periods is offset by the nth part of the measuring range of a sensor element, where n is number of beat angle periods.
US 2015/226581 discloses an arrangement for measuring an angular position of a rotor with respect to a stator. This arrangement comprises a multi-pole magnet mounted on the rotor, a sensor mounted on the stator and a plurality of sensor elements organized in two groups or four groups for measuring a magnetic field component. A method for calculating the angular position based on the signals of the elements of each group is disclosed. Thus, a magnetic sensor can be provided that measures a magnetic field of a multipole magnet, while being substantially insensitive to a dipole field.